REMOTE-SENSING AEROSOLS USING SATELLITE INFRARED OBSERVATIONS

Aerosol detection techniques using infrared wavelengths have a distinc t advantage over visible techniques by providing coverage over bright surfaces and during the night. This study investigates detection of vo lcanic and soil-derived aerosols, two important aerosols in studies of the earth's climate, using infrared observations at the following app roximate wavelengths 8.5, 11, and 12 mu m. Detection is based on brigh tness temperature differences among the three channels BT11-BT12 and B T8-BT11 It is demonstrated that these three infrared channels are usef ul for detecting stratospheric volcanic aerosols over oceans. Theoreti cal simulations agree with observations from current satellite instrum ents. Detection of the stratospheric aerosol over land is complicated by spectral variation of surface emissivity. Retrieving aerosol optica l depth over land requires defining the surface spectral emittance. De tecting the presence of soil-derived aerosols can also be aided with i nfrared observations. Increasing the dust optical depth increases BT11 -BT12 and BT8-BT11. The effect is opposite to that of an H2SO4 stratos pheric aerosol and differs from an increase in atmospheric precipitabl e water, though addition of ice clouds moves the differences in the sa me direction. Retrievals of aerosol optical depth over the desert must account for surface emissivity and the vertical distribution of the d ust. Negative differences in BT11-BT12 are observed to occur for dust storms over the Arabian Peninsula, Africa, and the southwest United St ates and is useful for remote sensing source regions of dust outbreaks . These negative differences can be simulated using the theoretical mo del but requires a specific dust aerosol model. There are inconsistenc ies between theoretical simulations of the infrared properties of heav y dust loadings and the satellite observations. Negative differences i n BT11-BT12 are useful for detecting and tacking dust storms.